A method for calculating the gas production of a shale gas well after pressure boosting

Abstract

The application discloses a kind of shale gas well pressure-increasing post-production gas quantity calculation method, belong to shale gas development technical field, including the following steps: obtaining target well parameters, target well parameters include: wellhead daily gas production before pressure-increasing, wellhead pressure before pressure-increasing, wellhead pressure after pressure-increasing;Calculate the formation pressure of target well;Draw inflow curve, outflow curve before pressure-increasing, outflow curve after pressure-increasing;Obtain wellhead daily gas production after pressure-increasing;Calculate and obtain incremental gas production;The present application uses equivalent permeability instead of complex fracture network, deduces simplified and applicable calculation formula of shale gas, which considers matrix linear flow, fracture geometric parameters and desorption effect of shale gas, and can quickly obtain formation pressure;Using the characteristics that formation pressure changes little before and after pressure-increasing, wellhead daily gas production is obtained through the change of outflow curve, and the calculation result has high accuracy.

Description

Technical Field

[0001] This invention relates to the field of shale gas development technology, and more specifically, to a method for calculating the increased gas production after pressurization of a shale gas well. Background Technology

[0002] Shale gas extraction typically goes through a phase of high production in the early stage, rapid decline in the middle stage, and low and stable production in the later stage. As gas is extracted from the well, the formation pressure continues to decrease, and the bottom hole flowing pressure also decreases. When the wellhead pressure is close to or lower than the pressure of the external transmission pipeline, the gas in the well cannot enter the external transmission pipeline, resulting in a large amount of remaining reserves that cannot be extracted economically and effectively.

[0003] Pressure enhancement is a key technical measure to maintain well productivity and increase economic returns (EUR) during the mid-to-late stage development of shale gas fields. After pressure enhancement, the wellhead pressure and bottomhole flowing pressure are significantly reduced, and the pressure difference between the formation and the bottom of the well increases, thereby increasing the flow rate of gas from the formation to the bottom of the well and thus increasing daily gas production. This measure can effectively extend the economic life of gas wells. Therefore, accurately predicting the changes in daily gas production after pressure enhancement is crucial for optimizing the timing of pressure enhancement, evaluating the effect of pressure enhancement, adjusting the production system, and formulating the overall development strategy of the gas field.

[0004] Currently, the prediction of daily gas production after pressurization mainly relies on empirical methods and numerical simulation methods. However, due to the significant differences in production regimes, gas flow states, and reservoir conditions before and after pressurization, empirical methods have obvious limitations. As for numerical simulation methods, the stress sensitivity coefficient, fracture conductivity attenuation law, and low-pressure seepage parameters required are difficult to obtain accurately in real time during gas well production. Furthermore, gas wells may exhibit different sensitivities in the low-pressure stages before and after pressurization. Therefore, the prediction results obtained through numerical simulation methods also have strong uncertainties. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problem that the prediction results obtained by using existing methods to predict the daily gas production change of shale gas wells are not accurate, and to propose a method for calculating the increased gas production after pressurization of shale gas wells.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for calculating the increased gas production after pressurization of a shale gas well includes the following steps: Obtain the target well parameters, including: daily gas production at the wellhead before pressurization. Wellhead pressure before pressurization Wellhead pressure after pressurization ; Calculate and obtain the formation pressure of the target well ; Plot the inflow curve, the outflow curve before pressurization, and the outflow curve after pressurization; Obtain the daily gas production at the wellhead after pressurization ; Calculate the increase in gas production .

[0007] Furthermore, the target well parameters also include: the number of effective fractures. Dimensionless matrix permeability Units: mD, effective reservoir thickness Unit: m, crack spacing Unit: m, crack half-field Unit: m, formation temperature Unit: kJ, gas viscosity Units: mPa·s, gas deviation factor Dimensionless, bottom hole flowing pressure before pressurization Units: kPa, rock bulk density Units: t / m³, Langmuir volume Units: m³ / t, Langmuir pressure Units: kPa, porosity Dimensionless gas compressibility coefficient Unit: kPa -1 .

[0008] Furthermore, the calculation obtains the formation pressure of the target well. The steps include: based on the daily gas production at the wellhead before pressurization. Bottom-hole flowing pressure before pressurization Based on the IPR calculation formula for multi-stage fracturing in shale gas horizontal wells, the formation pressure of the target well is calculated in reverse. ; The IPR calculation formula for multi-stage fracturing in shale gas horizontal wells is as follows: , In the formula: Indicates the daily gas production at the wellhead; This indicates the bottom hole flowing pressure.

[0009] Furthermore, the step of plotting the inflow curve includes: based on formation pressure The IPR calculation formula for multi-stage fracturing in shale gas horizontal wells is used to plot the inflow curve; the inflow curve is used to characterize the daily gas production at the wellhead. With formation pressure The relationship between them.

[0010] Furthermore, the step of plotting the outflow curve before pressurization includes: based on the bottom hole flowing pressure before pressurization. Plot the pressure value on the vertical axis and the daily gas production at the wellhead on the horizontal axis. Plot the outflow curve before pressurization on the horizontal axis.

[0011] Furthermore, the step of plotting the outflow curve after pressurization includes: Based on the wellhead pressure after pressurization Pressure drop calculation model to calculate and obtain bottom hole flowing pressure after pressurization. ; Based on the bottom hole flowing pressure after pressurization Plot the pressure value on the vertical axis and the daily gas production at the wellhead on the horizontal axis. Plot the outflow curve after pressurization on the horizontal axis.

[0012] Furthermore, the pressure drop calculation model adopts one of the following: the Beggs-Brill model, the Hagedorn-Brown two-phase flow pressure drop model, and the original Gray model.

[0013] Furthermore, the x-axis corresponding to the intersection of the outflow curve and the inflow curve before pressurization is the daily gas production at the wellhead before pressurization. The x-axis corresponding to the intersection of the outflow curve and the inflow curve after pressurization is the daily gas production at the wellhead after pressurization. Increase gas production =Daily gas production at the wellhead after pressurization - Daily gas production at the wellhead before pressurization .

[0014] The beneficial effects of this invention are as follows: The method for calculating the increased gas production after pressurization of a shale gas well provided by this invention uses equivalent permeability to replace the complex fracture network, deriving a simplified calculation formula applicable to shale gas. This calculation formula considers the linear flow of the matrix, fracture geometric parameters, and the desorption effect of shale gas. The calculation parameters are relatively easy to obtain, the calculation process is simple, and the formation pressure can be obtained quickly. This method takes advantage of the small change in formation pressure before and after pressurization, and obtains the daily gas production at the wellhead through the change in the outflow curve. It can be calculated for different single well production conditions, and the calculation results are highly accurate. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a method for calculating the increased gas production after pressurization of a shale gas well, provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the inflow curve and the outflow curves before and after pressurization in an embodiment of the present invention; Figure 3 This is a schematic diagram of the inflow curve and outflow curve before and after pressurization of well J1 in an embodiment of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0018] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0019] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0020] Please see Figures 1 to 3 The illustrated embodiment of this application provides a method for calculating the increased gas production after pressurization of a shale gas well. In practical applications, this method is used to predict the daily gas production at the wellhead of the target shale gas well after pressurization and compare it with that before pressurization to obtain the increased gas production.

[0021] It should be noted that the following assumptions are made in the embodiments: 1. Assume that the flow of shale gas from the matrix to the fracture is a pseudo-steady-state linear flow, which mainly occurs within the fracturing zone (SRV).

[0022] The above assumptions are based on the fact that shale gas exists primarily in an adsorbed state within shale. During extraction, pressure reduction leads to gas desorption, which then flows through microfractures and the matrix into the artificial fracture network. Therefore, the flow process can be divided into three stages: desorption, matrix diffusion, and fracture seepage. The process of gas flowing from the matrix into the fractures and then into the wellbore may initially be linear flow, but later it becomes quasi-steady. Horizontal well IPR curves typically describe the relationship between daily gas production and pressure under steady-state or quasi-steady-state conditions. Among the multiple flow stages in the shale gas well production lifecycle, the quasi-steady-state linear flow stage is usually the longest-lasting and most productive stage, potentially lasting for months or even years. Therefore, establishing a production capacity model for this main stage is of the most practical value for medium- and long-term production forecasting, recoverable reserve assessment, and economic analysis.

[0023] 2. Assume the artificially created fractures near the wellbore after fracturing the target well are as follows: including... Equal-length symmetrical vertical effective cracks, with a crack half-length of Total length of crack Equal to the effective thickness of the reservoir Crack spacing Control the discharge width of a single crack to make the discharge zone rectangular, i.e., long... The width of the discharge zone is 2 .

[0024] 3. Assume the reservoir is a homogeneous gas reservoir; the purpose is to optimize the calculation process. Since the fracture length and extension after fracturing are very complex, they cannot be realized through simple calculation. Numerical simulation can simulate the fracture extension, but it cannot completely restore the actual situation of the fracture, and the calculation process requires a large number of parameters.

[0025] 4. Assume fluid properties As a constant, the pseudo-pressure Simplified The purpose is to ultimately obtain a concise analytical solution; the pseudo-pressure It is a mathematical function with specific physical meaning defined to simplify the gas seepage equation, taking into account fluid properties. The influence of flow makes Darcy's law for gases as simple in form as that for liquids; in the derivation, when the product of gas viscosity and deviation factor is assumed to be constant, the pseudo-pressure simplifies to a square function of pressure. The difference is used to approximate the actual pressure difference.

[0026] 5. Assuming the shale gas desorption process conforms to the Langmuir isotherm, the amount of adsorbed gas... .

[0027] Shale gas mainly consists of adsorbed gas and free gas. Free gas is gas that exists freely in cracks and pores and is the primary gas supplier in the early stages of production. Adsorbed gas is gas that is adsorbed on the shale surface and cannot move freely. It can be desorbed from the rock surface to supply gas after the pressure drops to a certain level. The amount of adsorbed gas... This refers to this portion of the gas; the Langmuir volume and Langmuir pressure are obtained through testing, and empirical values ​​can also be used when rapid acquisition is required.

[0028] 6. Neglect wellbore friction, non-Darcy flow, and stress sensitivity effects.

[0029] This application provides a method for calculating the increased gas production after pressurization of a shale gas well, which includes the following steps: Obtain the target well parameters, including: daily gas production at the wellhead before pressurization. Wellhead pressure before pressurization Wellhead pressure after pressurization The wellhead pressure before pressurization Wellhead pressure after pressurization Used to plot outflow curves, which describe the relationship between shale gas production and pressure loss during flow within the wellbore.

[0030] In this step, the target well parameters obtained also include: the number of effective fractures. Dimensionless matrix permeability Units: mD, effective reservoir thickness Unit: m, crack spacing Unit: m, crack half-field Unit: m, formation temperature Unit: kJ, gas viscosity Units: mPa·s, gas deviation factor Dimensionless, bottom hole flowing pressure before pressurization Units: kPa, rock bulk density Units: t / m³, Langmuir volume Units: m³ / t, Langmuir pressure Units: kPa, porosity Dimensionless gas compressibility coefficient Unit: kPa -1 .

[0031] Calculate and obtain the formation pressure of the target well .

[0032] In this step, based on the daily gas production at the wellhead before pressurization... Bottom-hole flowing pressure before pressurization Based on the IPR calculation formula for multi-stage fracturing in shale gas horizontal wells, the formation pressure of the target well is calculated in reverse. Specifically, the IPR calculation formula for multi-stage fracturing in shale gas horizontal wells is as follows: , In the formula: Indicates the daily gas production at the wellhead; This indicates the bottom hole flowing pressure.

[0033] Draw the inflow curve; In this step, based on formation pressure The IPR calculation formula for multi-stage fracturing in shale gas horizontal wells is used to plot the inflow curve; the inflow curve is used to characterize the daily gas production at the wellhead. With formation pressure The relationship between them.

[0034] Plot the outflow curve before pressurization; In this step, based on the bottom hole flowing pressure before pressurization... The node analysis method was adopted, with the pressure value as the vertical axis and the daily gas production at the wellhead as the horizontal axis. Plot the outflow curve before pressurization on the x-axis. The intersection of the outflow curve and the inflow curve before pressurization is the stable operating point of the target well before pressurization. The corresponding x-axis represents the coordinated production rate, which simultaneously satisfies the pressure loss balance of the upstream inflow section and the downstream outflow section, i.e., the daily gas production at the wellhead before pressurization. .

[0035] Plot the outflow curve after pressurization; In this step, several different daily gas production rates at the wellhead are given. According to the wellhead pressure after pressurization The pressure drop calculation model was used to calculate and obtain several bottom hole flowing pressures after pressurization. ; Based on the bottom hole flowing pressure after pressurization Plot the pressure value on the vertical axis and the daily gas production at the wellhead on the horizontal axis. To plot the outflow curve after pressurization on the horizontal axis, please refer to [link / reference]. Figure 2 .

[0036] In the above technical solution, the wellhead pressure after pressurization The process capacity is determined by the booster equipment and the throughput, based on the power of the booster equipment used and the wellhead pressure before boosting. Daily gas production at the wellhead before pressurization Predictive acquisition; bottom hole flowing pressure after pressurization Based on the wellhead pressure after pressurization Including the pressure drop in the vertical wellbore, the pressure gradient prediction for multiphase flow in the vertical pipe uses a pressure drop calculation model. As one implementation method of this application, the pressure drop calculation models include: the Beggs-Brill model, the Hagedorn-Brown two-phase flow pressure drop model, and the original Gray model. The selection of the pressure drop calculation model is based on the measured bottom hole flow pressure before pressurization. The pressure drop calculation model is compared with the bottom hole flowing pressure in the pressure drop calculation model, and the closest pressure drop calculation model is selected for calculation.

[0037] Obtain the daily gas production at the wellhead after pressurization .

[0038] In this step, the x-axis corresponding to the intersection of the outflow curve and the inflow curve after pressurization is the daily gas production at the wellhead after pressurization. .

[0039] Calculate the increase in gas production =Daily gas production at the wellhead after pressurization - Daily gas production at the wellhead before pressurization .

[0040] As one embodiment of this application, the increased gas production after pressurization of a pressurized shale gas well J1 is selected. Perform the calculations and verification; The target well parameters are obtained as follows:

[0041] The target well parameters are input into the IPR calculation formula for multi-stage fracturing in shale gas horizontal wells to obtain the formation pressure. : , Formation pressure =5900kPa.

[0042] For plotting the inflow curve and the outflow curve before pressurization, please refer to [link / reference]. Figure 3 ; Based on the type of booster pump used in the target well, the wellhead pressure can be reduced by 1000 kPa after boosting. The wellhead pressure after boosting is... =900kPa, the outflow curve after pressurization was calculated and plotted using nodal analysis.

[0043] Daily gas production at the wellhead before pressurization =11900m 3 / d, daily gas production at the wellhead after pressurization =19400m 3 / d, increased gas production =19400-11900=7500m 3 / d.

[0044] The release and migration of desorbed gas requires a time process, which may lead to overestimation of the predicted results in the early stages of production and underestimation in the later stages. This invention ignores the transient process of desorption, assuming that desorption is instantaneous and completely balanced with pressure. Once the bottomhole flowing pressure decreases, the adsorbed gas is instantly converted into free gas and ready to enter the fracture. The technical solution of this application uses equivalent permeability to replace the complex fracture network, deriving a simplified calculation formula applicable to shale gas. This calculation formula considers the linear flow of the matrix, fracture geometry parameters, and the desorption effect of shale gas. The calculation parameters are easy to obtain, the calculation process is simple, and the formation pressure can be obtained quickly. This method takes advantage of the small change in formation pressure before and after pressurization, and obtains the daily gas production at the wellhead through the change of the outflow curve. It can be calculated for different single well production conditions, and the calculation results are highly accurate.

[0045] The derivation process of the IPR calculation formula for multi-stage fracturing in shale gas horizontal wells is as follows: Based on Darcy's law, the equation of state for a real gas is derived as follows: (1) The equation of state for a gas under standard conditions is: (2) Dividing the two equations yields the underground volumetric flow rate. Compared with standard volumetric flow rate The relationship is (3) According to Darcy's law for linear flow, the underground volumetric flow rate... for (4) Combining equations (3) and (4), we can obtain (5) To each and Integrating and simplifying, we can obtain the formula for the flow rate of a one-sided linear flow under standard conditions. (6) Substitution achievable (7) A fissure is supplied with gas from both sides, therefore the total output of a single fissure is twice the flow rate from one side: (8) The production of free gas in the matrix pores is (9) Adsorbed gas on the surface of organic matter is an important component of shale gas. When the pressure decreases, the adsorbed gas desorbs and becomes free gas, supplementing production capacity. According to the Langmuir equation, the amount of adsorbed gas... It can be represented as (10) Its derivative This represents the amount of gas desorbed when the pressure drops by a unit value: (11) In mass equilibrium, the effect of desorbed gas can be analogized to the addition of a desorption compressibility factor. Then the overall compression coefficient Gas compressibility coefficient With desorption compression coefficient sum: (12) The contribution of desorption to production capacity is reflected as a correction factor greater than 1. Its value is the overall compression ratio. With gas compressibility The ratio: (13) Correction factor Multiplying by formula (9) and correcting the free gas production, we obtain the total production capacity equation as follows: (14) The above calculation formula is derived in imperial units. After conversion to metric units, it becomes the IPR calculation formula for multi-stage fracturing of shale gas horizontal wells in this invention.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for calculating the increased gas production after pressurization of a shale gas well, characterized in that, Includes the following steps: Obtain the target well parameters, including: daily gas production at the wellhead before pressurization. Wellhead pressure before pressurization Wellhead pressure after pressurization ; Calculate and obtain the formation pressure of the target well ; Plot the inflow curve, the outflow curve before pressurization, and the outflow curve after pressurization; Obtain the daily gas production at the wellhead after pressurization ; Calculate the increase in gas production .

2. The method for calculating the increased gas production after pressurization of a shale gas well according to claim 1, characterized in that, The target well parameters also include: the number of effective fractures. Dimensionless matrix permeability Units: mD, effective reservoir thickness Unit: m, crack spacing Unit: m, crack half-field Unit: m, formation temperature Unit: kJ, gas viscosity Units: mPa·s, gas deviation factor Dimensionless, bottom hole flowing pressure before pressurization Units: kPa, rock bulk density Units: t / m³, Langmuir volume Units: m³ / t, Langmuir pressure Units: kPa, porosity Dimensionless gas compressibility coefficient Unit: kPa -1 .

3. The method for calculating the increased gas production after pressurization of a shale gas well according to claim 2, characterized in that, The calculation obtains the formation pressure of the target well. The steps include: based on the daily gas production at the wellhead before pressurization. Bottom-hole flowing pressure before pressurization Based on the IPR calculation formula for multi-stage fracturing in shale gas horizontal wells, the formation pressure of the target well is calculated in reverse. ; The IPR calculation formula for multi-stage fracturing in shale gas horizontal wells is as follows: ， In the formula: Indicates the daily gas production at the wellhead; This indicates the bottom hole flowing pressure.

4. The method for calculating the increased gas production after pressurization of a shale gas well according to claim 3, characterized in that, The step of drawing the inflow curve includes: based on formation pressure The IPR calculation formula for multi-stage fracturing in shale gas horizontal wells is used to plot the inflow curve; the inflow curve is used to characterize the daily gas production at the wellhead. With formation pressure The relationship between them.

5. The method for calculating the increased gas production after pressurization of a shale gas well according to claim 3, characterized in that, The step of plotting the outflow curve before pressurization includes: based on the bottom hole flowing pressure before pressurization. Plot the pressure value on the vertical axis and the daily gas production at the wellhead on the horizontal axis. Plot the outflow curve before pressurization on the horizontal axis.

6. The method for calculating the increased gas production after pressurization of a shale gas well according to claim 3, characterized in that, The step of plotting the outflow curve after pressurization includes: Based on the wellhead pressure after pressurization Pressure drop calculation model to calculate and obtain bottom hole flowing pressure after pressurization. ; Based on the bottom hole flowing pressure after pressurization Plot the pressure value on the vertical axis and the daily gas production at the wellhead on the horizontal axis. Plot the outflow curve after pressurization on the horizontal axis.

7. The method for calculating the increased gas production after pressurization of a shale gas well according to claim 6, characterized in that, The pressure drop calculation model adopts one of the following: the Beggs-Brill model, the Hagedorn-Brown two-phase flow pressure drop model, and the original Gray model.

8. The method for calculating the increased gas production after pressurization of a shale gas well according to claim 1, characterized in that, The x-axis corresponding to the intersection of the outflow curve and the inflow curve before pressurization is the daily gas production at the wellhead before pressurization. The x-axis corresponding to the intersection of the outflow curve and the inflow curve after pressurization is the daily gas production at the wellhead after pressurization. Increase gas production =Daily gas production at the wellhead after pressurization - Daily gas production at the wellhead before pressurization .

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